Fuel cell and control unit in a detachable housing

ABSTRACT

The invention relates to a vehicle ( 1 ) with a fuel cell ( 2 ) for producing power. The vehicle has a monitoring and switching unit ( 18 ) which is detachably attached to the fuel cell housing, in a housing ( 19 ).

[0001] The invention relates to an apparatus having at least one fuelcell, which is intended for producing electrical power, and withelectrical power being distributed to electrical loads which arearranged in a high-voltage line network that is connected to the fuelcell, and being distributed to further electrical loads which arearranged in a low-voltage line network, which is connected to thehigh-voltage line network via at least one DC/DC converter and, inaddition to the loads, contains at least one rechargeable battery.

[0002] Mobile devices such as vehicles with a fuel cell for producingelectrical power often have two electrical line networks. A high-voltagenetwork, which is fed from the fuel cell, contains the relativelyhigh-power loads such as one or more traction motors and loads which arerequired for operating the vehicle when at rest or when in motion, aswell as electrical drives for auxiliary equipment for starting and foroperating the fuel cell which, by way of example, is in the form of aPEM fuel cell. The second network is a low-voltage network withrelatively low-power electrical loads, which are switched on as requiredduring motion or when the mobile device is stationary. The low-voltagenetwork is also connected to drives and other loads, such as heatingcircuits or a battery, which are required for starting the fuel cell.The low-voltage network contains a rechargeable battery which suppliesthe electrical power to the appropriate electrical loads for startingthe fuel cell. Bidirectional DC/DC conversion is provided between thetwo networks and, during operation, supplies charging current from thefuel cell for the rechargeable battery and, when required, operatingcurrent for loads that are connected in the low-voltage network. Whileone pole of the low-voltage network is connected to the mobile apparatusearth, the high-voltage network is electrically isolated.

[0003] The invention is based on the problem of specifying a compactappliance which can be handled on its own and can be installed in anapparatus such that it can be replaced and which carries out monitoringfunctions for electrical variables, distribution functions for the loadsand disconnection functions in order to prevent damage in the event ofcritical operating states as well as switching functions during thephases in which the fuel cell is being started and switched off, for thefuel cell, for the loads and for the line network, in the apparatuswhich contains a fuel cell for producing power and contains at least onenetwork with electrical loads that are supplied with power from the fuelcell.

[0004] The problem with an apparatus having at least one fuel cell,which is intended for producing electrical power, and with electricalpower being distributed to electrical loads which are arranged in ahigh-voltage power network that is connected to the fuel cell, and beingdistributed to further electrical loads which are arranged in alow-voltage power network, which is connected to the high-voltage powernetwork via at least one DC/DC converter and, in addition to the loads,contains at least one rechargeable battery, is solved according to theinvention in that a central monitoring and switching unit, which can behandled on its own, has a housing which can be attached in an easilydetachable manner to the fuel cell housing and in which conductors,which are in each case connected to an electrical output or pole of thefuel cell, are arranged via dust-tight and water-tight bushings in thewall of the housing and detachable contact means, of which conductors atleast one has a contact of a fuel cell circuit breaker in the course ofthe line, in that outgoers run from the conductors, which are providedwith fuses in at least one pole, to dust-tight and water-tight bushingsin a housing wall with detachable contact means, to which lines fromloads are connected, which loads are supplied with power from the fuelcell, in that one outgoer from the low-voltage line network runs via adust-tight and water-tight bushing to a control and evaluation unitwhich is associated with the central monitoring and switching unit andis connected to sensors for detecting the operating states of the fuelcell and of the electrical line networks, and via dust-tight andwater-tight bushings and easily detachable contact means in or on ahousing wall to sensors by means of which operating states of the mobileapparatus are detected, and in that the control and monitoring unitcloses the fuel cell circuit breaker once the fuel cell has been startedand has reached its operational readiness, and, on detection ofoperating states, which are measured by the sensors and correspond tocritical operating states which can be predetermined, for which thesupply of the high-voltage line network with power must be connected ordisconnected, opens the fuel cell circuit breaker. The functions whichare essential for controlling and monitoring the electrical linenetworks and their loads are carried out by components in an appliancewhich can be extended and can be checked on its own. Fast functionaltesting and fault localization are thus possible. The appliance can bemanufactured at low cost as a unit which can be handled on its own, andcan be installed in the mobile device quickly and easily. The bushingsprevent the ingress of moisture. The way in which the appliance operatesis thus not adversely affected even during operation or when located ina moist atmosphere. A control, and evaluation unit has already beenproposed in German Patent Application 199 500 08.8. Reference is herebymade to this patent application from the same applicant.

[0005] The control and evaluation unit can be arranged in the interiorof the housing, together with the other components of the centralmonitoring and switching unit, since it can be handled as a component ofthe central monitoring and switching unit. These other components of themonitoring and switching unit form a switching and distribution unit. Inone preferred embodiment, the control and evaluation unit is arranged inits own housing, which has the bushing for the outgoer for thelow-voltage network and the bushings for the easily detachable contactmeans in or on the housing wall for the line connections for the sensorsfor detecting the operating states, and in one of whose housing wallsplug connectors are arranged with connections for lines by means ofwhich the control and evaluation unit is connected to the sensors fordetecting the operating states of the fuel cell and of the electricalline networks, in which case the dedicated housing can be attacheddetachably, as a cover for an opening on the housing which can beattached to the fuel cell housing. In this embodiment, the control andevaluation unit forms a unit which can be handled on its own and can beinstalled and disconnected even without disconnecting the centralmonitoring and switching unit, that is to say this unit can also beproduced, tested, stored and transported, which is advantageous, atleast with regard to spares stockholdings.

[0006] It is particularly advantageous for the housing of the controland evaluation unit to be thermally insulated from the housing with thecomponents of the switching and distribution unit. The control andevaluation unit may therefore contain electronic components whoseoperating temperature is not significantly adversely influenced by theoperating temperature of the fuel cell. For example, large-scaleintegrated electronic circuits such as processors may be provided in thecontrol and evaluation unit.

[0007] In one highly advantageous embodiment, the control and evaluationunit has a printed circuit board which is provided with electroniccomponents and is arranged in the interior of a trough-shaped cover,which covers the housing, which is open on one side, with the componentsof the switching and distribution unit, with a thermally insulatinginsert in front of the opening in the housing. In this embodiment, whenthe housing is open, both the interior of that part of the monitoringand switching unit which has the power distribution, fuse and switchingelements, that is to say the switching and distribution unit, and thecontrol and evaluation unit in the cover are easily accessible, thusconsiderably simplifying and facilitating testing, inspection andmaintenance.

[0008] The apparatus is preferably designed to be mobile. In particular,the apparatus is a motor vehicle which is supplied with power from afuel cell. However, it may also be any other mobile apparatus, such as aboat, ship, locomotive, prime mover or the like.

[0009] The water-tight bushings and the easily detachable contact meansare preferably in the form of water-tight plug connectors. The plugconnectors are secured in particular by means of “interlock” connectionsagainst being mated and disconnected while on load. These plugconnectors allow not only quick production and disconnection of thecontacts but also protection against the ingress of dust, water ormoisture into the housing interior.

[0010] One other option is to provide water-tight line bushings which,at least at their ends which are arranged outside the housing, havecable lugs for attachment to the associated ends of the line networks.

[0011] In one preferred embodiment, the control and evaluation unit isconnected to gas sensors, which are arranged outside the housing, forthe detection of leaks in units which produce hydrogen, store hydrogenor carry hydrogen, to a sensor, which is arranged in the housing withthe power distribution, fuse and switching elements, for the fuel cellcurrent, to at least one sensor which is arranged outside the monitoringand switching unit and detects an impact between the mobile device andan obstruction, to an arrangement, which is arranged in the housing withthe power distribution, fuse and switching elements, for measurement ofthe insulation resistance of the electrically insulated line network, toa sensor, which is arranged in the monitoring and switching unit, forthe fuel cell voltage, and opens the fuel cell circuit breaker when ameasured value is detected which is undesirable or unacceptable forsafety reasons. The control and evaluation means, which are provided foroperational safety and reliability of the fuel cell system and of theline network, are arranged protected in housings, in this embodiment.When a measured value such as this is detected, the control andevaluation unit opens the fuel cell circuit breaker to change the fuelcell system to a state in which the power output from the fuel cell isinterrupted, that is to say the line network together with theelectrical loads is changed to a safe operating state. This avoids anydanger to personnel, parts of the apparatus itself and, in conjunctionwith this, the entire apparatus with the fuel cell system as well as theenvironment. In one particularly expedient embodiment with a monitoringand switching unit to which a control and evaluation unit having ahousing in the form of a cover is connected, plug connectors whichdisconnect the lines to the loads when the cover is disconnected arearranged on the cover edges, in which case the housing, which is in theform of a cover, can be connected by means of plug connectors to thelines to the loads. When the cover is removed, the voltage isdisconnected from the lines to the loads, provided that the loads do notinclude an energy store, such as a battery or a capacitor.

[0012] The control and evaluation unit monitors, in particular, the fuelcell output current for overshooting a limit value which can bepredetermined, possibly monitors the current of the electrical drive andthe voltages of the fuel cell and possibly monitors the low-voltagenetwork for overshooting or undershooting limit values which can bepredetermined, and monitors the insulation resistance for undershootinga value which can be predetermined.

[0013] It is expedient for the housing to be arranged at a point in themobile device which is not adversely affected, or is adversely affectedonly to a minor extent, in the event of mechanical destruction of themobile device.

[0014] The control and evaluation unit preferably comprises integratedcircuits which are arranged on a printed circuit board in the housing.The conductors and outgoers in the housing interior may be in the formof a cable harness, in the form of conductors using stamped gridtechnology, in the form of conductor tracks on a printed circuit board,for example a multilayer printed circuit board, in the form of copperrails, or in the form of flexible circuit technology. The nature of theconductors and outgoers depends on the magnitudes of the currents whichare being distributed. Two or more of the techniques mentioned above mayalso be used in the housing.

[0015] In one preferred embodiment, the fuel cell can be switched off,in particular by means of detachable contacts, via a line which can bedisconnected from the connection to the fuel cell housing when thehousing is removed. This embodiment is a safety circuit. The safetycircuit can be formed by a link via two plug contacts, or may be in theform of a separately routed line to the high-voltage supply.

[0016] It is particularly expedient for the housing of the monitoringand switching unit and/or the fuel cell housing to have centring orguide means for interlocking attachment of the housing to the fuel cellhousing. The housing can thus be fitted to the fuel cell quickly andeasily, in the position in which it is held.

[0017] The housing of the monitoring and switching unit can be screwedto the fuel cell housing, or can be attached by latching means. Themechanical attachment of the housing to the fuel cell housing isphysically simple, and can thus be produced or detached easily.

[0018] Direct attachment of the housing of the monitoring and switchingunit to the fuel cell housing results in short line sections between theelectrical outputs of the fuel cell and the fuel cell circuit breaker,which is in the form of a power switch. The joining direction of thehousing may be chosen to match the available space on the fuel cell, andto be at an easily accessible point. The housing of the centralmonitoring and switching unit can be attached to the fuel cell housingin a particularly rigid manner. There is no need for it to be held in aparticular manner on other parts of the mobile device. The coupling ofthe housing to the fuel cell housing means that the retention of thefuel cell housing in the mobile device is sufficient for both housings,so that the housing of the monitoring and switching unit is coupled, interms of vibration and oscillations, to the fuel cell.

[0019] The nature of the attachment and the location of the housing ofthe monitoring and switching unit allow the housing to be fitted andremoved easily and quickly. Servicing and repair work can thus becarried out not only with the monitoring and switching unit installedbut also with it removed. The monitoring and switching unit can beinstalled and removed without removal of other parts of the mobile unit.

[0020] It is expedient for a dedicated housing, or at least acompartment for fuses in the conductors and their outgoers, to bearranged within the housing of the monitoring and switching unit and tobe accessible through an opening, which can be sealed, in the housing ofthe monitoring and switching unit. With a device such as this, fuses canbe replaced easily and quickly, without having to remove the housing.The fuse holders are, in particular, mounted on a printed circuit board.Depending on the size of the line cross sections of the lines running tothe fuse holders, and on the number of fuses, it is also possible to useinsulated lines, stamped grids composed of electrically highlyconductive materials, conductor rails or flexible circuits withconductor tracks. The fuses for the high-voltage line network arepreferably arranged in the fuse housing, and are accessible via anopening, which can be sealed, from outside the housing of the monitoringand switching unit. This opening can be sealed in particular by means ofthe cover-like housing of the control and evaluation unit. This allowsthe fuses for the high-voltage line network to be accommodated in a safeand sealed manner. The compartment with the fuses for the outgoers ofthe high-voltage network expediently has an additional cover in thehousing of the central monitoring and switching unit. This providessafety against accidentally touching them after opening the housing ofthe monitoring and switching unit.

[0021] The fuses are expediently arranged on a printed circuit boardunder the cover, which can be sealed, of the housing of the centralmonitoring and switching unit.

[0022] The low-voltage line network and the high-voltage line networkare DC networks, that is to say they have two poles. Since one pole ofthe low-voltage line network is connected to the mobile device earth, asingle-pole fuse is sufficient for the network and load lines. Theoutgoers and loads in the high-voltage line network may have single-poleor two-pole protection.

[0023] The drive motor or motors for the propulsion system as well asthe upstream converter and other electrical loads are protected, inparticular, in the interior of the monitoring and switching unit.

[0024] If a particularly rugged housing is required for the monitoringand switching unit, the housing is produced from metal. One advantage ofa housing such as this is also the good thermal conductivity, that is tosay the heat which is produced in the housing is dissipated well. Theamount of heat emitted to the exterior can be increased further by meansof cooling ribs or heat exchangers in some other form.

[0025] A very strong housing can also be produced by means of a housingcomposed of a high-strength resistant plastic, which also allows theweight to be reduced. A housing such as this is expediently composedpartially of metal, if the heat is intended to be dissipated to theexterior via the highly thermally conductive metal. The housing sectionwhich is composed of metal has, in particular, cooling ribs.

[0026] In a further preferred embodiment, the housing of the monitoringand switching unit has a switch, for example a microswitch, or sensorson housing openings, which responds when the housing cover is opened,opening the fuel cell circuit breaker. The influence on the fuel cellcircuit breaker when the switch is opened can be produced byinterrupting the holding current for the fuel cell circuit breaker, thatis to say the switch on the opening of the housing is arranged, forexample, in the circuit of the coil for the fuel cell circuit breaker.Once the fuel cell circuit breaker has opened, there is no voltagewithin the housing, except for low-voltage circuits and the linesections from the outputs of the fuel cell to the contacts of the fuelcell circuit breaker. Instead of the switch on the housing cover, it isalso possible to use a sensor, for example a light barrier etc. If thecontrol and evaluation unit is arranged in the cover for the housing ofthe monitoring and switching unit, then there is no current to the fuelcell circuit breaker when the cover is removed, so that the high-voltageline network is not live.

[0027] The fuses for the low-voltage line network circuits can likewisebe arranged in the housing of the monitoring and switching unit. In acase such as this, they are expediently arranged so that they areaccessible from the outside and are separated from the fuses for thehigh-voltage line network. However, it is also possible to arrange thefuse for the low-voltage line network in an externally accessiblehousing which is separate from the housing of the monitoring andswitching unit. The fused switches are, for example, arranged on aprinted circuit board. The fuse holders may also be connected to copperrails or to flexible lines or to flexible circuits with conductortracks. An arrangement in which the connections for the fuse holders usestamped grid technology is likewise possible.

[0028] The fuse housing for the low-voltage line network is, by way ofexample, integrated in the low-voltage line network. However, a separatefuse housing is advantageous, which is externally accessibleindependently of the housing of the monitoring and switching unit.

[0029] The DC/DC converter device, which by way of example is arrangedbetween the high-voltage line network and the low-voltage line networkas a bidirectional converter, may require a precharging current in orderto start to operate. The precharging components may be arranged in thehousing of the monitoring and switching unit. If no precharging optionis required, the space reserved for these components in the housingremains free. Another advantageous arrangement for the equipment of themonitoring and switching unit is for the components to be installed intheir own housing, which can be fitted externally to the housing of themonitoring and switching unit, with water-tight bushings and plugconnectors being provided for the electrical connection in the twohousings.

[0030] The fuel cell circuit breaker for isolating the fuel cell fromthe loads and from a hybrid battery or supercapacitor may have twopoles, with both poles being circuit breaker poles for interruptingshort-circuits. However, it is also possible to design the contact foronly one pole to switch full-load and short-circuit currents. The othercontact is then only in the form of an isolating switch, which does nothave to switch high currents. In this case, the second contact can beopened with a certain delay with respect to the first contact, since thefirst contact switches higher currents. One contact may then be a switchwithout contacts, for example a semiconductor switch. A single-pole fuelcell circuit breaker may also be used, which is designed for switchingthe maximum load current and the short-circuit current.

[0031] In order to simplify servicing and repair of components of themobile device, and to allow this to be carried out without any dangerfrom live objects, it is expedient to provide a manually operable offswitch in the housing of the monitoring and switching unit, in whichcase the off switch can be operated from the outside without removingthe housing. This allows the high-voltage line network, together withits electrical loads, to be conductively isolated from the fuel cell. Itis expedient to provide an additional switch, which is externallyaccessible, for any hybrid battery or supercapacitor which may be used.

[0032] The invention will be described in more detail in the followingtext with reference to exemplary embodiments which are described in adrawing and from which further details, features and advantages willbecome evident. In the figures:

[0033]FIG. 1 shows, schematically, a mobile apparatus with a fuel cellfor producing electrical power, and with loads which are connected to aline network that is supplied from the fuel cell,

[0034]FIG. 2 shows a block diagram of a central monitoring and switchingunit, which is arranged in a mobile device and is detachably connectedto a fuel cell,

[0035]FIG. 3 shows a perspective view of a central monitoring andswitching unit whose housing is attached to the housing of the fuelcell,

[0036]FIG. 4 shows, schematically and in the form of a section, acentral monitoring and switching unit with another housing embodiment,

[0037]FIG. 5 shows, schematically and in the form of a section, acentral monitoring and switching unit with a further housing embodiment.

[0038] A mobile device 1, in particular a vehicle, contains a fuel cell2 which may be in the form of a PEM cell and comprises a stack ofindividual fuel cell modules. The fuel cell 2 feeds electrical loadsand, for example, at least one energy store such as a hybrid battery orsupercapacitor, via a two-pole line network 3. Since the fuel cell 2 isformed from a relatively large number of individual modules, a higheroutput voltage is emitted during normal operation.

[0039] The line network 3 is therefore referred to as a high-voltageline network 3 or as a high-voltage network 3. The high-voltage network3 is connected via a converter 4 to a drive motor 5 which, for example,drives the wheels of the mobile device 1 which may, by way of example,be a vehicle. The network 3 is connected via a converter, which is notidentified in any further detail, to a drive motor 6 for a compressor,which is provided with air for supplying the fuel cell 2. Furthermore,the network 3 is connected to a bidirectional DC voltage interface, forexample a bidirectional DC/DC converter 7, which has a furtherinput/output to the vehicle power supply network 8, whose operatingvoltage is lower than that of the high-voltage network 3. The vehiclepower supply network 8, which is also referred to as a low-voltagenetwork 8, is connected to a rechargeable battery 9, which can beconnected, for example via switches, to the DC/DC converter 7. Thelow-voltage network 8, whose operating voltage is, for example, 12 or 14V, has a number of electrical loads, of which only a windscreen wipermotor 12, a fan motor 13 and a heater 14 are illustrated in FIG. 1. Afurther vehicle power supply network with a voltage of 36 V or a networkat 24 V for an LAN or bus may also be provided. The fuel cell 2 can beconnected to the high-voltage line network 3 via, for example, atwo-pole fuel cell circuit breaker 15. A fan motor 16 and a pump motor17 are connected to the network 3, for example via converters which arenot identified in any more detail. Further loads which are notillustrated, and a hybrid battery or supercapacitor 10, may also beconnected to the high-voltage network 3. The supercapacitor 10 can bedisconnected from the line network 3, in particular by means of an offswitch 11.

[0040] The mobile apparatus 1 has a central monitoring and switchingunit 18 which is not shown in any more detail in FIG. 2. The centralmonitoring and switching unit 18 is located in a housing 19, which isattached in an easily detachable manner to the housing 20 of the fuelcell 2. The fuel cell 2 has two electrical outputs 21, 22 or poles,which are connected to a plug connector 23, which is designed to bewater-tight. A corresponding plug connector part 24 is located on thehousing 19, and its contacts, which are not identified in any! moredetail, are connected in a two-pole configuration via conductors 25, 26to the contacts of an off switch 27, which can be operated by hand bymeans of a handle which projects out of the housing 19. When the offswitch 27 is opened, the entire high-voltage network 3 locateddownstream from the off switch 27 is rendered non-live, except, forexample, for battery or capacitor subscribers which can be switched offseparately so that servicing, maintenance or repair work can be carriedout on or in the mobile device, without removing the housing 19 andwithout any danger from live parts.

[0041] Downstream from the off switch 27, the conductor runs 25, 26 eachhave a mate contact 28 of a first fuel cell circuit breaker 29, and amate contact 30 of a second fuel cell circuit breaker 31. The matecontact 28 is followed by a conductor 32, and the mate contact 30 isfollowed by a conductor 33. The conductors 25, 36, 32 and 33 arecomponents of the high-voltage network 3, which is an electricallyisolated network, that is to say an unearthed network. Two single-polefuel cell circuit breakers 29, 31 improve the disconnection safety incomparison to a two-pole fuel cell circuit breaker with poles which areoperated jointly, since the probability that the two switches cannot beoperated is less than the probability of failure of one switch. The offswitch 27 may be omitted if precautions are taken to ensure that thefuel cell circuit breakers 29, 31 can be operated, that is to saydisconnected, by hand. A monitoring and switching unit 18 without aseparate off-switch is shown in FIG. 1. A housing 34 with fuse holdersand fuses, which will be described in more detail in the following text,is located in the interior of the housing 19. The conductor 32 isconnected to a current sensor 35 which has a current transformer 36which has an annular core, through which a power conductor is passed,without making contact. Outgoers 37, 38, 39, 40, 41 originate from theconductor 32 downstream from the current transformer 36. Outgoers 42,43, 44, 45, 46 originate in a corresponding manner from the conductor33. The outgoers 37 to 41 run into the interior of the housing 34 tofuse holders having fuses, which are not identified in any more detail.Conductors run from the fuse holders of these fuses and from theoutgoers 42 to 46 to a plug connector 47 in the wall of the housing 19.Pairs 37, 42 and 38, 43; 39, 44, 40, 45 and 41, 46 form outgoer lines toloads in the mobile device 1. The outgoer lines 37, 39, 40 and 41 areprovided with fuses, which are not identified in any more detail and,together with the outgoer line 43 with the outgoers 42, 43, 44, 45, 46,are intended for the connection of external lines to the housing 18,which originate from the loads and have plug connectors 48 at the ends,which correspond to the plug connector 47. The plug connector 47 isdesigned to be water-tight, in the same way as the plug connector 24.The outgoer lines 37, 42 and 39, 44; 40, 45; 41, 46 are connected, forexample, to the converter 4, and to the converters for the fan and pumpmotors 16, 17 and for the DC/DC converter 7. The outgoers 38, 43 areconnected to the drive unit, which contains a separate protectiondevice, by means of the converter and the drive or traction motor 6.

[0042] The outgoers which are illustrated in FIG. 2 are indicated onlyas an example, for illustrative purposes. There may also be moreoutgoers depending on the number of high-voltage loads in the mobiledevice.

[0043] The conductors 25, 26, 32, 33 and the outgoers 37 to 44 as wellas the conductors which run from the fuse holders in the housing 34 tothe plug connector 47 are in the form of insulated conductors,conductors produced using stamped grid technology, or copper rails.Printed conductor tracks on boards or flexible circuits may also beprovided. The configuration of the conductors using one of thetechniques which have been mentioned depends on the number of theseconductors and on the conductor cross sections that are required.

[0044] The fuel cell circuit breakers 29, 31 are circuit breakers andare designed for disconnecting the full-load current and theshort-circuit current. Tripping with only a single-pole fuel cellcircuit breaker is also possible.

[0045] Since the mate contacts 28, 30 must open when the fuel cellsystem or the vehicle is in critical states, the provision of twocontacts, which can be operated independently of one another, provides ahigher level of confidence that one contact will operate in the event ofa defect in the other, thus disconnecting at least one pole of thenetwork.

[0046] The coils of the fuel cell circuit breakers 29, 31 and/orcontactors or relays are each connected to outputs of a control modulein the form of an economizer 49 and of an economizer 50. The twoeconomizers 49 and 50, which are arranged on a printed circuit board 51and [lacuna] to a control and evaluation unit 52, which will beexplained in more detail in the following text and is part of thecentral monitoring and switching unit 18, are circuits which produce ahigher power for operation, that is to say for pulling in, of DCcontactors or relays, and then emit the lower holding voltage for thecircuit breakers 28, 31 or relays. A relay driver module 53 is alsolocated on the printed circuit board 51, and is connected to a relay 54which is not on the printed circuit board 51. The driver module 53 hastwo inputs, one of which is connected via a diode 55, which is arrangedon the printed circuit board 51, to a plug connector 56, on the housing19, to which a key-operated switch is connected, by means of which thevehicle is started. When the key-operated switch is closed, the voltagefrom the vehicle low-voltage network 8 is applied to one input of thedriver module 53. This low-voltage network is the normal power supplynetwork for vehicles and contains a rechargeable battery 9 with avoltage of, for example, 12 V, 14 V, 24 V or 36 V. Loads in thislow-voltage network include, for example, windscreen wiper motors, fanmotors, window winder motors, lamps, indicator lights, etc. The relay54, which is also referred to as the system relay, supplies, once it hasoperated, electronic components on the printed circuit board 51 via itscontact with the operating voltage of, for example, 12-14 V, 24 V or 36V.

[0047] There is also a further driver module 56 on the printed circuitboard 51 which is fitted, in particular, with the components of thecontrol and evaluation unit 52, and this further driver module 56 hastwo inputs, with a relay 57, which is not located on the printed circuitboard 51 and is outside the housing 19, being connected to its output.One conductor track 60 on the printed circuit board 51 is connected viaa plug connector 51 in the housing 19 to the low-voltage network 8,which is connected to the housing 19 via a plug connector, which is notidentified in any more detail. A number of components on the printedcircuit board 51 are connected to the conductor track 60. Theconnections for the operating power supply for the economizers 49, 50are connected to the conductor track 60. The connection for theoperating power supply for the driver stage 53 is connected to theconductor track 60 via a diode, which is not identified in any moredetail. Furthermore, one connection of a power supply unit 61 isconnected to the conductor track 60. The second connection of the powersupply unit 61 is connected to the vehicle earth. The power supply unit61 is in the form of a DC/DC converter and has no conductive connection,as indicated in the drawing by the transformer symbol, between the inputvoltage and the output voltage. The power supply unit 61 uses theoperating voltage of, for example, 12 or 14 V from the vehicle powersupply network to produce a higher voltage of, for example, 15 V. Therelay 57 is intended to control the precharging of the DC voltage/DCvoltage interface, and has a contact 58 which is connected in parallelwith one of the mate contacts 28 or 30, in series with a resistor. Thecoil of the relay 57 is connected via a plug connector 80 to the drivermodule 56 and to the conductor track 60. The series-connected contact 58and resistor 81 are connected by means of plug connectors to lines inthe housing, which form a circuit in parallel with the mate contact 30.

[0048] The printed circuit board 51 is subdivided into two sections 63,64 in terms of the operating voltage and the voltage levels of thecomponents arranged on it, thus physically isolating the components atthe different voltage levels. This provides a high level of safety withregard to short-circuits between components and lines, or conductortracks at different voltage levels.

[0049] Evaluation electronics 62 and a bus interface 65 are located onthe section 63 which is associated with the low voltage level. Theevaluation electronics include a logic circuit 66, which has a number ofinputs, and whose connection to components will be described in moredetail in the following text. On the output side, the logic circuit 66is connected to control inputs of the economizers 49, 50 and of thedriver modules 53, 56.

[0050] The fuel cell system has gas sensors for hydrogen, in order tomonitor the fuel. These gas sensors require operating voltages whichdiffer from the voltage in the low-voltage network 8. In general, theoperating voltage is less than the vehicle power supply network voltage.The signals which are produced by the gas sensors are at least not atthe same voltage level as the vehicle power supply network or in theregion of the input signals which can be processed by the logic circuit63. Analogue converter and matching circuits 67, 68 are thus provided onthe printed circuit board 51. The converter and matching circuits 67, 68each have outputs, which are not identified in any more detail, to whichthe operating voltage connections of gas sensors, which are notillustrated in any more detail, are connected via plug connectors, whichare not identified in any more detail, in the housing 19. Furthermore,the converter and output circuits 67, 68 each have two inputs, which arenot identified in any more detail but are connected to plug connectorsin the housing 19, for the analogue signals which are emitted from thegas sensors. The outputs of the converter and output circuits 67, 68 areconnected to one input of the logic circuit 66 and one input of aprocessor 69, which is preferably a microprocessor. This input of theprocessor 69 may be an analogue input with a downstream A/D converter.One input of the logic circuit 66 is designed for threshold valuedetection, that is to say the output signals from the converter andmatching circuits 67, 68 are processed further by the logic circuit 66only if they are beyond a certain level. The converter and matchingcircuits 67, 68, the logic circuit 66 and the processor 69 are arrangedwith their appropriate connections on the printed circuit board 51 forexternal components and for conductor tracks between the connections andthe inputs of these components in the section 63. The logic circuit 66has further inputs, which are connected to plug connectors 70 of thehousing 19. Switching contacts, for example, are connected to theseinputs. These switching contacts are used, for example, to monitorwhether apparatuses in or on the vehicle are closed. One switchingcontact 71, which is supplied with voltage from the vehicle power supplynetwork 8, is provided for monitoring a cover of the housing 19. Furtherinputs of the logic circuit 66 are connected via the plug connector 70in particular to sensors for AIRBAGS and other sensors which detect andsignal collisions of the mobile device or of the vehicle. A furtherinput, which is not identified in any more detail, of the logic circuit66 is connected to an emergency off switch via the plug connector 70. Atleast one input of the logic circuit 66 is connected to a correspondingoutput of the processor 69.

[0051] The processor 69 has inputs which are not identified in any moredetail and are connected via a plug connector 72 on the housing 19 to abus, to which other subscribers in the vehicle are also connected. Thebus is preferably the CAN bus which is known per se. A serial interfaceof the processor 69 can be connected to appropriate transmissionappliances. Furthermore, the processor 69 has a BOOT input, which is notidentified in any more detail. The reference potential for thosecomponents which are arranged on the section 63 is the vehicle earthpotential.

[0052] The current transformer 36 is mounted on the section 64. Thecurrent transformer 36 is part of the current sensor 35, which measuresthe fuel cell current using the compensation principle which is knownper se. The current sensor 35 is connected, for example, via amultiplexer that is not illustrated, to an A/D converter 73, which isconnected by means of an optocoupler to the processor 69. Furthermore,at the output, the current sensor 35 has an optocoupler, which is notidentified in any more detail but whose output is connected firstly toone input of the processor 66, and secondly to one input of the logiccircuit 63. The A/D converter 73 is connected to one input, for example,via the multiplexer, and a line which is not illustrated is connected tothe positive output 21 or to the negative output 22.

[0053] A device 74 for measuring the isolation resistance between theelectrically isolated network and the mobile device or vehicle earth islocated in the section 64. The isolation resistance is represented bydashed lines in the drawing, and is annotated 75. The referencepotential for those components which are arranged in the section 64 isthe potential of the positive or negative output 21, 22 of the fuel cell2. The isolation resistance 75 is measured using a pulsed method.

[0054] During the isolation measurement, the processor 69 receives anumber of measured values of the voltage across the measurementresistor, only after a specific waiting time, which is matched to thetransient time of the measurement system, averages these measured valuesin order to minimize low-frequency interference, and then calculates theisolation resistance. During operation of the mobile device or of thevehicle, when the voltage at the output of the power supply unit 61 isavailable, the isolation resistance of the unearthed network of the fuelcell 2 is measured continuously. In the event of unacceptabledeteriorations in the isolation, the processor 69 causes the switchingcontacts 28, 30 of the switches 29, 31 to open, via the logic circuit63.

[0055] The current transformer 36 has an additional winding, into whicha defined current is fed from a current source, in order to check theserviceability of the current transformer and of the optocoupler,including the serviceability of the conductor tracks as far as theprocessor 69.

[0056] The logic circuit 66 has hardware logic functions of acombinational and sequential nature, and possibly memory functions, thusensuring that the input signals are processed quickly. This means that,in critical situations in and on the mobile device or on the vehicle, orin the event of dangers to the vehicle occupants, which are signalled byappropriate sensors, the logic circuit 66 very quickly processes andpasses on the appropriate messages, causing the switching contacts 28,30 and 58, respectively, to open, via the economizers 49, 50 and 56,respectively. Voltage is thus removed from the high-voltage network 3together with the loads which are connected to it, so that it is nolonger possible for any danger to originate from a dangerous voltage.

[0057] The detection of a short-circuit current in the fuel cell networkis reported to the processor 69 and, via the logic circuit 66, resultsin immediate tripping, that is to say opening, of the switching contacts28, 30 and of the contact, if this is in the closed state.

[0058] The monitoring measures described above and the separation of theprinted circuit board 51 into a low-voltage section 63 and ahigh-voltage section 64 achieve a high level of safety on their own. Thedevice 74 for measurement of the isolation resistance is controlled oractuated from the processor 69 via an optocoupler interface, which isnot shown in any more detail. This also applies to the A/D converter 73and to the current sensor 35.

[0059] All the inputs and outputs of the components on the section 63are resistant to short-circuits to the vehicle earth and to the 12 V, 14V or 24/26 V voltage and, in the event of a short-circuit, can bedetected as faults which are signalled and, in addition to thesignalling in the case of those short-circuits which adversely affectthe safety of operation and of the vehicle in an unacceptable manner,lead to opening of the switching contacts 28, 30. The relay 57 with thecontact 58 and the resistor 81 as well as the associated conductortracks and plug connectors are located in a dedicated housing 80 a,which can be detachably attached to the housing 19 and is optionallyconnected to the housing 19, when precharging of circuits and convertersor transformers is required.

[0060] The low-voltage network 8 has outgoers, of which only two areidentified by 76, 77, in the housing 19. The outgoers have protectivedevices 78, 79, so that the outgoers are resistant to short-circuits.The outgoers are connected via plug connectors, which are not identifiedin any more detail, to a controller in the mobile device 1. Theshort-circuit-resistant outgoers form the interface from 12-14 V to thecontroller.

[0061] All the plug connectors on the housing 19 comply at least withIngress Protection Class IP 67 in accordance with DIN 40050, that is tosay protection against direct contact with live parts, against theingress of dust and against the ingress of water. Those components whichare required for monitoring of the electrical variables relating to thefuel cell and to the line networks 3 and 8 are located on the printedcircuit board 52.

[0062] Water-tight cable bushings may also be provided, instead of theplug contacts described above. However, plug contacts have the advantagethat the lines can be withdrawn easily, so that the monitoring andswitching unit 16 can be removed more quickly. The components of themonitoring and switching unit 19 are designed in accordance with themotor vehicle standard.

[0063] The housing 19 is attached to the housing 20 by means of twocentring strips, which are not identified in any more detail, and screws82, two of which are illustrated in FIG. 2.

[0064] When the housing 19 is inserted into the centring strips on thehousing 20, the plug connectors 23, 24 are mated. The rigid connectionbetween the two housings 19, 20 results in the central monitoring andcontrol unit 18 forming a unit which oscillates with the fuel cell 2, sothat there is no need for any dedicated mounting, that is capable ofoscillation, in the mobile device 1 or in the vehicle.

[0065] The conductors 32, 33 and 37 to 44 are preferably arranged withthe fuse holders on a central distribution printed circuit board in thehousing 19. The fuse holders together with the fuses are arranged underthe cover 83 of the housing 19. There is also a cover on the fuses sothat, when the cover is opened, the fuses and fuse holders cannot betouched until the additional cover is removed. The housing 19 may befitted in the mobile device 1 or on the vehicle such that it can beopened from its underneath.

[0066] The housing 19 may be composed of metal or of a resistantplastic, or of a combination of both. The low-voltage line network 8 mayhave a fuse board 84, which is represented by dashed lines in FIG. 1, inthe housing 19 or at some other point in the device 1. The arrangementin the housing 19 has the advantage that all the fuses are located at acentral point. The lines to the fuses for the low-voltage network 8 canbe connected by means of plug connectors, which are not shown. A line 85which loops via the fuel cell housing 20 and is passed via plugconnectors between the housings 19, 20 is opened when the housing 19 isremoved. This line 85 is connected to the logic circuit 66, which opensthe fuel cell circuit breakers 29, 30 when the line 85 is opened.

[0067] Plug connectors, for example 47, are arranged in the wall in thelower part of the housing 19. The plug connectors are connected to thewall in a dust-tight and water-tight manner. The cover 83 also coversthe side walls of the housing and has openings in the region of the plugconnectors.

[0068]FIG. 4 shows a central monitoring and switching unit 86, which hasa housing 87 for power distribution, switching elements and fuses in thehigh-voltage line network 3 and a housing 88 in which the control andevaluation unit 52 is located, which forms a part of the monitoring andswitching unit 86. Identical parts in FIGS. 1-5 are provided with thesame reference symbols. The switching elements, conductor tracks,outgoers, and fuses on the high-voltage side of the monitoring andswitching unit 86, that is to say the switching and distribution unit,are identified in general by 89 in FIG. 4. One face of the housing 87,which is in the form of a box, has an opening which extends entirely, oressentially entirely, over that face, although this is not identified inany more detail. This opening can be sealed by the housing 88, which isin the form of a trough, that is to say it has a U-shaped cross section.The depth of the housing 88 is intended to accommodate components of thecontrol and evaluation unit 52, whose printed circuit board 52 isarranged in the housing interior, parallel to the flat board face of thehousing 88, which forms a cover for the housing 87. The opening in thehousing 89 is also covered by a thermally insulating panel 90. Plugconnectors 91, 92 and 93, 94, respectively, are located at the edges ofthe housings 87 and 88. When the housings 87, 88 are connected to oneanother, the plug connectors 91 and 93 engage in one another in the sameway as the plug connectors 92 and 94. The connections between theelectrical components of the control and evaluation unit 51 and theelectrical components of the switching and distribution unit, which islocated in that part of the monitoring and switching unit 86 which isidentified as 89, run via the plug connectors 91, 93.

[0069] The connections between the outgoers of the high-voltage linenetwork 3 and the loads as well as the hybrid battery and/or thesupercapacitor are passed via the plug connectors 92, 94. These outgoerlines run within the housing 88 to plug connectors 95 on one sidehousing wall. Lines which are not illustrated in any more detail but areequipped with appropriate plug connectors at the ends run from the plugconnectors 95 to the loads and to the hybrid battery. Further plugconnectors 96 on the housing 88 are provided for the connection of lineswhich connect the sensors described above in the mobile device to thecomponents of the switching and monitoring unit 52. When the housing 87is opened by removing the housing 88, which is in the form of a cover,the electrical connections for the loads and for the hybrid battery areinterrupted, so that the loads are not live. There is then no longer anyneed to operate a special off switch. Furthermore, the control linesbetween the switching and monitoring unit 52 and the battery circuitbreakers are interrupted, so that the contacts of the battery circuitbreakers are opened owing to the lack of the coil voltage. Both theinterior of the housing 87 and the housing 88 are then accessible, andthere is no need for a dedicated cover monitoring switch. The housing 87is connected to the fuel cell housing in a manner as illustrated in FIG.3.

[0070]FIG. 5 shows a form of a housing 97, which is somewhat modifiedfrom the apparatus shown in FIG. 4 in terms of the connections, with thecomponents of the switching and distribution unit of a switching andmonitoring unit 98 and of a housing 99 for the control and evaluationunit 51, whose printed circuit board 52 is arranged within the housing99. The trough-shaped housing 99 forms the cover for the housing 97which is open on one side, since, at the lower edge, it contains plugconnectors 100 for connection of the outgoers to lines which run to theloads and/or to the hybrid battery or the supercapacitor.

[0071] A heat-insulating panel 103 separates the interior of the housing97 from the interior of the housing 99. Seals 104 are provided betweenthe edges of the openings of the housings 97 and 99. On one face, whichis set back with respect to the side wall of the housing 97 locatedabove it, the housing 99 has plug connectors 105 for the lines tosensors and/or signalling and indication elements, or to other bussubscribers in the mobile device.

1. Apparatus having a fuel cell for producing electrical power and withthe electrical power being distributed to electrical loads which arearranged in a high-voltage line network which is connected to the fuelcell, and being distributed to further electrical loads which arearranged in a low-voltage line network, which is connected to thehigh-voltage line network via a DC/DC converter, characterized in that acentral monitoring and switching unit (18) has a housing (19) which canbe mounted detachably on the fuel cell housing (20) and in whichelectrical conductors (25, 32; 26, 33), which are connected via bushingsin one housing wall (19) and contact means to in each case oneelectrical output (21, 22) of the fuel cell (2), are arranged, and ofwhich conductors at least one (25, 32) has a contact (28) of a fuel cellcircuit breaker (29), in that the conductors (32, 33) are connected toloads via outgoers (37-46), which (37-41) are provided with fuses in atleast one pole, and via bushings in one housing wall (19) and contactmeans, in that the low-voltage line network (8) is connected via abushing to a control and evaluation unit (52) which is associated withthe central monitoring and switching unit (18), in that the control andevaluation unit (52) is connected via bushings in one housing wall (19)and contact means to sensors for detecting operating states (2) of theapparatus, and in that the bushings in the housing walls (19) aredust-tight and water-tight and the contact means are detachable. 2.Apparatus according to claim 1, characterized in that the control andevaluation unit (52) closes the fuel cell circuit breaker (28, 29) whenthe fuel cell (2) reaches operational readiness and/or, on detection ofoperating states, which are measured by the sensors and correspond tocritical operating states which can be predetermined, opens the fuelcell circuit breaker (28, 29).
 3. Apparatus according to claim 1,characterized in that the control and evaluation unit (52) is arrangedin the interior of the housing (19), together with the other componentsof the central monitoring and switching unit (18).
 4. Apparatusaccording to claim 1, characterized in that the control and evaluationunit (52) is arranged in its own housing (88, 99), which is fitted as acover for an opening on a housing (87, 97) in which a switching anddistribution unit (89) for the central monitoring and switching unit(86, 98) is located.
 5. Apparatus according to at least one of thepreceding claims, characterized in that the housing (88, 99) of thecontrol and evaluation unit is thermally insulated from the housing (87,97) with the components of the switching and distribution unit (89) forthe central monitoring and switching unit (86, 98).
 6. Apparatusaccording to at least one of the preceding claims, characterized in thatthe control and evaluation unit (52) has a printed circuit board (51)which is fitted with electronic components and is arranged in theinterior of the housing. (88, 99) which is in the form of atrough-shaped cover and has an opening facing the opening of the housing(87, 97) with the components of the switching and distribution unit(89).
 7. Apparatus according to at least one of the preceding claims,characterized in that said apparatus is in the form of a motor vehicle.8. Apparatus according to at least one of the preceding claims,characterized in that the dust-tight and water-tight bushings and theeasily detachable contact means are plug connectors (23, 24, 47, 56, 59,70, 72).
 9. Apparatus according to at least one of the preceding claims,characterized in that the control and evaluation unit (52) is connectedto gas sensors, which are arranged outside the housing, for thedetection of leaks in units of the mobile device which produce hydrogen,store hydrogen or carry hydrogen, to a sensor (35) for the fuel cellcurrent, to at least one sensor which detects an impact between themobile apparatus and an obstruction, to a device (74) for measurement ofthe insulation resistance of the electrically insulated high-voltageline network (3), to a sensor for the fuel cell voltage and to a sensorfor measurement of the voltage of the low-voltage line network (8), andopens the fuel cell circuit breaker (28) when a measured value isdetected which is undesirable or unacceptable for safety reasons. 10.Apparatus according to claim 9, characterized in that the control andevaluation unit (52) monitors the voltages of the high-voltage network(3) and of the low-voltage network (8) for limit values which can bepredetermined being overshot or undershot, the fuel cell output currentfor overshooting a limit value which can be predetermined, and theinsulation resistance of the high-voltage network (3) for undershootinga limit value which can be predetermined.
 11. Apparatus according to atleast one of the preceding claims, characterized in that the housing(19) is arranged at a point which is not adversely affected, or isadversely affected only to a minor extent, in the event of mechanicaldestruction of the mobile device.
 12. Apparatus according to at leastone of the preceding claims, characterized in that the control andevaluation unit (52) comprises integrated circuits which are arranged ona printed circuit board (51) in the housing (19; 88; 99).
 13. Apparatusaccording to at least one of the preceding claims, characterized in thatthe fuel cell (2) can be switched off via a line (85) which can bedisconnected from the connection to the fuel cell housing (20) when thehousing (19) is removed.
 14. Apparatus according to at least one of thepreceding claims, characterized in that the housing (19; 88; 99) and/orthe fuel cell housing (20) have centring or guide means for interlockingattachment of the housing (19) to the fuel cell housing (20). 15.Apparatus according to at least one of the preceding claims,characterized in that the housing (19; 88; 99) can be screwed to thefuel cell housing (20), or can be attached by latching means. 16.Apparatus according to at least one of the preceding claims,characterized in that the housing (19; 88; 99) can be rigidly attachedto the fuel cell housing (20).
 17. Apparatus according to at least oneof the preceding claims, characterized in that a dedicated housing (34)for fuses in the outgoers (37-42) is arranged in the housing (19; 88;99) of the monitoring and switching unit (18).
 18. Apparatus accordingto claim 17, characterized in that the fuses of the high-voltage linenetwork (3) are arranged in a fuse housing, and are accessible via anopening, which can be closed, from outside the housing (19) of themonitoring and switching unit (18).
 19. Apparatus according to claim 17or 18, characterized in that the fuses are arranged on a printed circuitboard underneath the cover, which can be sealed, of the housing (19) ofthe monitoring and switching unit (18).
 20. Apparatus according to atleast one of the preceding claims, characterized in that the converterfor the drive motor (5) for the mobile device (1) is protected by a fusein the housing (19).
 21. Apparatus according to at least one of thepreceding claims, characterized in that the housing (19; 88; 99) iscomposed of metal.
 22. Apparatus according to at least one of claims 1to 20, characterized in that the housing (19; 88; 99) is composed ofplastic.
 23. Apparatus according to at least one of claims 1 to 20,characterized in that the housing (19) is composed of metal and plasticparts.
 24. Apparatus according to at least one of the preceding claims,characterized in that the housing (19) of the monitoring and switchingunit (18) has a switch (71) or sensor on the housing opening, whichresponds when the housing cover is opened and opens the fuel cellcircuit breaker (28, 30).
 25. Apparatus according to at least one of thepreceding claims, characterized in that the fuses for the circuits ofthe low-voltage line network (8) are arranged in the housing (19). 26.Apparatus according to at least one of claims 24, 25, characterized inthat the fuses for the circuits of the low-voltage line network (8) arearranged in fuse holders on a printed circuit board.
 27. Apparatusaccording to at least one of the preceding claims, characterized in thatcomponents for the precharging of the DC/DC converter (7) are arrangedin a housing (80 a) on the housing (19) of the monitoring and switchingunit (16).
 28. Apparatus according to at least one of the precedingclaims, characterized in that a manually operable off switch (27) isarranged in the housing (19; 88; 99), upstream of the fuel cell circuitbreaker (29, 30) in the course of the conductors (25, 32; 26, 33).